The invention relates to an adjusting device for a disc brake and, more particularly, an adjusting device for a pneumatically actuated disc brake with a rotary lever-actuated brake application device, which adjusting device can preferably be inserted in an adjusting spindle of the brake application device and can be attached to a brake caliper of the disc brake by way of a mounting disc.
Adjusting devices or wear adjustors for disc brakes are available in different designs. From DE 10 2004 037 771 A1 (having U.S. published counterpart application US2009/209890 A1) an adjusting device for a disc brake is known, the specifications of which are expressly incorporated by reference herein. This adjusting device is suitable for a pneumatically actuated disc brake, more preferably in one having floating or sliding caliper design. However, it can also be utilized in pneumatically actuated fixed or pivoting caliper disc brakes.
Pneumatically actuated disc brakes have over time become standard equipment on heavy commercial vehicles. Such disc brakes require a mechanical boosting or “force amplification” for generating the required clamping force since the force of pneumatically actuated brake cylinders is limited because of the pressure level (currently approximately 10 bar) and the limited size of the brake cylinders. The currently known pneumatically actuated disc brakes have amplification ratios between 10:1 and 20:1. The piston strokes of the brake cylinders range from 50 to 75 mm, which produces clamping travel for pressing the brake pads against the brake disc of approximately 4 mm.
The friction material thickness of the brake pads is in the range of 20 mm, since two pads are installed, a wear travel of approximately 40 mm thus being obtained without consideration of the disc wear. This travel is a multiple greater than the above-mentioned clamping travel. It is therefore necessary to adjust the brake by means of a device in accordance with the pad wear. The state of the art is an automatically operating wear adjustment, by which it is achieved that the so-called lift clearance, meaning the air gap between the brake pads and the brake disc in the unactuated stated, is kept constant independently of the wear state and wear characteristic of the brake pads.
Frequently, disc brakes having a wear adjustor that is arranged concentrically in the hollow space of a threaded spindle or ram and eccentrically driven by a rotary brake lever via a drive element (e.g., shifting finger) are very frequently found in commercial vehicles. During a braking operation, the brake lever coupled with the piston rod of the brake cylinder performs a rotary movement. Before the rotary movement of the lever is introduced into the wear adjustor via the coupling mechanism of the adjustment (e.g.: shifting fork and shifting finger or gears), a so-called idle travel has to be overcome. This travel is decisive for the size of the lift clearance since during this movement the adjustment is not activated and the clamping travel thus constitutes the lift clearance. Once this idle travel has been overcome, the adjustor is put into a rotary motion and an adjusting operation is initiated through the coupling to the threaded spindle or tube.
DE 10 2004 037 771 A1 describes such an adjusting device, which is shown in FIG. 5. It substantially consists of the following function elements: shaft 2; mounting disc 3; axial bearing 4; collar bush 5; shifting fork, or drive ring 6; ball ramp clutch 7; clutch ring 8; cone clutch 9; and cylindrical spring 10. With respect to the description, reference is made to DE 10 2004 037 771 A1.
Essentially, the wear adjusting device has to fulfil two functions:
1. the automatic lift clearance setting (normal operation); and
2. the manual resetting of the adjusting mechanism when replacing the brake pads.
When installing new brake pads, the thrust pieces, which press the brake pads against the brake disc, have to be retracted. This is carried out by turning back threaded spindles (threaded tubes), which during the use of the brake were turned out through the automatically operating wear adjustor in accordance with the brake pad wear.
During this turning back, the adjusting device is manually turned back with a spanner from the so-called wear position into the starting position. When doing so, the adjusting device has to be turned against the locking direction of a freewheel. However, since the freewheel has a 100% locking action, turning back is not easily possible.
This and other objects are achieved by an adjusting device for adjusting the wear of brake pads and a brake disc of a pneumatically actuated disc brake with a rotary lever-actuated brake application device. The wear adjustor preferably can be inserted in an adjusting spindle of the brake application device and attached to a brake caliper of the disc brake by way of a mounting disc. Axially on a side of a drive ring, an axial bearing, and axially on the opposite side of the drive ring, a ball ramp coupling with freewheel function is formed. The ball ramp coupling comprises balls, a drive bush arranged axially between the axial bearing and its balls on the drive end and a clutch ring on the output side. A cone clutch is arranged between the clutch ring on the output side and a spring sleeve for a cylindrical spring. Axially between the cone clutch and the spring sleeve, a torque-dependent coupling with positive restraint is arranged.
Because of this it is possible that installation space and interface targets are taken into account and largely maintained, as a result of which a simple replacement is possible. The torque-dependent coupling with positive restraint additionally offers a typical noise upon manual resetting as an acoustic feature, which in a simple manner already known to the user signals to an actuating person a certain state as a result of which a training process is simplified.
In that the cone clutch preferably is a ball cone clutch which comprises the drive-end clutch ring and a cone bush interacting with the torque-dependent coupling, wherein between the output-side clutch ring and the cone bush, cone balls are arranged, it is possible to achieve a compact design. More particularly, since the torque-dependent coupling is formed as a ratchet coupling from a portion of the cone bush of the cone clutch and a coupling disc. The positive restraints are formed from corresponding toothings in each case. The coupling disc is connected to the spring sleeve.
This design offers the following advantages:
(a) the known, typical noise occurs upon manual turning-back;
(b) by retaining a locking function of the freewheel in the rest position, an improved shake-proof feature against turning-open of the adjusting mechanism is obtained;
(c) cost-effective manufacture of the components is achievable through non-cutting forming.
In a preferred embodiment, the corresponding toothings are embodied on the portion of the cone clutch and on the coupling disc as opposing spur toothings. Such components can be cost-effectively produced through non-cutting forming.
Turning back or retraction of the adjusting device is carried out against the locking direction of the freewheel. The torque-dependent coupling through matching of the spur toothings makes possible that the toothings “over-ratchet” when a certain torque is exceeded. The preload of this coupling is performed via the cylindrical spring already present in the adjusting device, which cylindrical spring is preferably adjustable. The torque-dependent coupling is designed for a higher transmission moment than the ball ramp coupling. If the ratchet coupling were to respond before the ball ramp coupling, which can also be called a load shift coupling, major wear of the ratchet coupling would occur because of the high stress cycle numbers involved.
With this adjusting device, a directional coupling acting in the axial direction is installed. The directional coupling is formed of a ball ramp system and a friction coupling, more preferably the ball cone clutch.
Upon manual turning back, the rotary movement is initially introduced into the torque-dependent ratchet coupling and into the ball cone clutch via the shaft and the spring sleeve. From there, the torque is directed into the ball ramp coupling via the friction connection in the ball cone coupling. Since ball cone and ball ramp coupling are matched for retention by friction, a clamping effect occurs.
The clutch ring and the drive ring which are connected to the shifting fork or form a portion thereof, are each provided with an inner profiling with the help of which it is possible to prevent the two components in the rest position from turning back further. Support for the drive ring and the clutch ring is effected on a collar bush mounted in a rotationally fixed manner, which includes an outer profiling matching the inner profiling of the clutch ring and of the drive ring. When the introduced torque exceeds the response moment of the ratchet coupling, “ratcheting-through” of the ratchet coupling occurs. With stops of the outer profile on the inner profile of the drive ring and the clutch ring, it is achieved that on the one hand the clamping action of the freewheel is retained and on the other hand no rotation in the ball ramp coupling occurs. Otherwise the ratchet coupling would not respond immediately but the ball ramp coupling could be initially rotated until reaching an end position of the balls on the ramp tracks (torque of the ball ramp coupling<torque of the ratchet coupling).
In addition, it is provided that when positioning the stops of the inner profiles of the drive ring and the clutch ring, the stop of the outer profile of the collar bush with the inner profile of the drive ring becomes effective slightly earlier than the stop with the inner profile of the clutch ring. This is effected in that between the outer profile and the inner profiles an angular clearance for the advance of a stop between outer profile and drive ring inner profile before a stop between outer profile and clutch ring inner profile is formed.
It is furthermore preferred that the other end of the collar bush, which forms the fixed portion of the axial bearing, is fastened in a rotationally fixed manner to the mounting disc attached to the brake caliper.
The axial bearing is formed by the one side of the drive ring, rolling elements and a collar of a collar bush, which extends axially through the ball ramp coupling. This likewise reduces the number of components, and allows for a compact construction to be achieved.
A disc brake, more preferably a pneumatically actuated disc brake includes such an adjusting device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.